Unloader valve for air compressor

ABSTRACT

A valve device provided to the outlet port of an air compressor for subjecting the compressor to a limited back pressure until the compressor gains enough speed to be able to pick up the full load. Thereafter the device operates to open the passage to the compressed air tank. This device is provided with a casing having a main passage therethrough in which there is positioned a check valve which controls the passage to the compressed air tank. This device also includes a cylinder which is connected to the casing by a restriction hole and the cavity of this cylinder is normally open to the atmosphere. A valve member is provided in the cylinder cavity responsive to the flow of air into the cavity through said restriction hole and this valve member functions to close an exhaust hole when the air compressor approaches delivery of normal compressed air output. The check valve in the main passage is then opened and compressed air flows into the tank.

United States Patent [191 Smith 1 May 15, 1973 [54] UNLOADER VALVE FOR AIR COMPRESSOR [75] Inventor: Dresden G. Smith, San Jose, Calif.

[73] Assignee: Aqna-Mec, Inc., San Jose, Calif.

[22] Filed: May 28, 1971 [21] Appl. No.: 148,012

[52] U.S. Cl. ..137/512.3, 137/517, 137/519.5 [51] Int. Cl ..F16k 15/00 [58] Field ofSearch ..l37/5l2.3,5l7,5l9.5

[56] References Cited UNITED STATES PATENTS 2,511,494 6/1950 Cohen ..l37/512.3 X 2,444,182 6/1948 Calvin ..l37/5l2.3

Primary Examiner-Charles J. Myhre Assistant ExaminerFrank H. McKenzie, Jr. A ttorney Allen & Chromy [57] ABSTRACT A valve device provided to the outlet port of an air compressor for subjecting the compressor to a limited back pressure until the compressor gains enough speed to be able to pick up the full load. Thereafter the device operates to open the passage to the compressed air tank. This device is provided with a casing having a main passage therethrough in which there is positioned a check valve which controls the passage to the compressed air tank. This device also includes a cylinder which is connected to the casing by a restriction hole and the cavity of this cylinder is'normally open to the atmosphere. A valve member is provided in the cylinder cavity responsive to the flow of air into the cavity through said restriction hole and this valve member functions to close an exhaust hole when the air compressor approaches delivery of normal com pressed air output. The check valve in the main passage is then opened and compressed air flows into the tank.

2 Claims, 6 Drawing Figures PATENTED MAYI 5 197a sum 2 0 2 22b T DELIVERY FULL ZONE 40 TORQUE 39- SHIFT ZONE 25 250 2 VENT ZONE K l 37 L\ E 220 SPEED FULL SPEED-P L 5/ FIG. 4 N 4 TANK PRESSURE a B 3 BALL SHIFTS O COMPRESSOR SPEED- z FIG 5 o O o.5

I Q 0 IO 20 3o 40 so PSIG UNLOADER VALVE FOR AIR COMPRESSOR DESCRIPTION OF THE INVENTION This invention relates to a valve device for use on air compressors pumping air into a tank, to reduce the load on the compressor during start up.

An object of this invention is to provide an improved valve device for use on air compressors to reduce the load thereon during start up.

Another object of this invention is to provide a valve device in the outlet port of an air compressor which serves the purpose of allowing the compressor to be subjected to a limited back pressure until the motor driving the compressor gains enough speed to be able to assume the full load and thereafter the device opens a passage for compressed air to be supplied to the tank.

Another object of this invention is to provide a small air compressor with a device that automatically allows the compressor to be subjected to only a limited back pressure until the compressor motor gains enough speed so that the compressor can assume the full load of supplying air to a compressed air tank, said compressor being connected to the air tank through a check valve which is opened by the air pressure supplied by the compressor and air is thereafter pumped into the tank until a predetermined pressure is achieved.

Other and further objects of this invention will be apparent to those skilled in the art to which it relates from the following specification, claims and drawing.

In accordance with this invention, there is provided a valve device to a small compressor for the purpose of automatically controlling the load on the compressor motor until the motor attains a great enough speed to be able to assume the full load of the compressor pumping into a tank for compressed air. Small air compressors are generally provided with electric motors which do not have a sufficiently high starting torque to be able to operate an air compressor when the compressor is pumping air into a tank already having a quantity of compressed air therein. In this invention, there is provided a valve device that allows the motor to gain running speed before the compressor assumes full load. This device is provided with a casing having a main passage therethrough which is connected to the compressed air tank through a check valve that is spring-biased so that it is normally closed. The check valve is also subjected to any back air pressure that may be in the tank. The valve device is also provided with a cylindrical chamber which is provided with a cavity that is connected to the main valve passage by a restriction hole. The cylinder cavity is normally open to the atmosphere through an exhaust hole.

During starting of the compressor the compressed air therefrom passes from the main passage through the restriction hole into the cavity of the cylinder and flows outward through the exhaust hole. As the compressor gains speed more compressed air flows through the restriction hole into the cylinder cavity and a valve member positioned in this cavity closes the exhaust hole. This closing is accomplished against a spring-biased member that is positioned in a portion of the exhaust hole so that the compressor must be approaching normal speed before this exhaust hole is closed. After the exhaust hole is closed the compressed air output of the compressor opens the check valve to the compressed air tank and air is supplied thereto until a predetermined pressure is attained.

Further details and features of invention will be set forth in the following specification, claims and drawing in which briefly:

FIG. 1 is a vertical sectional view of an embodiment of this invention showing the parts thereof in normal position occupied thereby when the air compressor is started;

FIG. 2 is a vertical sectional view of the device similar to that shown in FIG. 1 with the valve parts thereof in the positions occupied when the compressor is operating under full load;

FIG. 3 is a fragmentary sectional view of another embodiment of this invention;

FIG. 4 is a graph showing the relation between the torque and speed of the compressor motor;

FIG. 5 is another graph showing the relation between the compressor speed and air pressure; and

FIG. 6 is a compressor performance curve showing the relation between the surface cubic feet per minute and the gage pressure per square inch.

Referring to the drawing in detail, reference numeral 10 designates a portion of the housing of an air compressor having an outlet port into which the casing 11 of a valve device is threaded. The casing 11 is provided with a main passage 12 which has an enlarged portion 13 in which the ball 14 of a check valve is positioned. A spring 15 presses on the ball 14 against the seat surface 16 when the compressor is idle and during start up. An expandable member 17 is lodged in a groove formed in the casing 11 and provides a stop for the spring 15 to retain this spring in the cavity 13 pressing against ball 14. Threads 18 are provided in the casing 11 to engage a suitable tubular member (not shown) leading to a compressed air tank (also not shown).

A restriction passage 19 opens into the main passage 12 and the enlarged portion of this restriction passage extends through the projection 11a of the casing. A plug 19a is threaded into the open end of passage 19. Laterally extending air-spreading channels 20 are provided to the projection 11a connecting with the restriction passage and these laterally extending passages open into the cylinder cavity 21 inside of the cylinder 22. The outside of the projection 11a is threaded and the cylinder 22 is attached thereto by suitable mating threads. A threaded nut 23 is positioned on the projection 11a and this nut is tightened against the bottom of the cylinder 22 when the cylinder is positioned on the projection 11a so that the bleeder passage 24 is just above the threaded portion of the projection 11a.

Laterally extending exhaust ports 25 are provided in the cylinder body and these ports connect to the passage 26 through which the valve rod 27 extends. The passage 26 is larger than the valve rod 27 and when this rod is in the position shown in FIG. 1 this passage forms a path for the air leaving the cylinder cavity 21 through the laterally extending exhaust ports 25. Rod 27 is provided with an enlarged portion 28 which is large enough to close the passage 26 when the valve rod is in the position shown in FIG. 2. In this position the O- ring 29 is against the end wall of the cavity 21 and forms a seal therewith.

The rod 27 is provided with an enlarged end portion 30 which abuts the O-ring 29 and presses this ring against the end wall of the cylinder when the rod is raised by air supplied to cavity 21 through the restriction passage 19. Two coil springs 31 and 32 are provided around the rod 27 and these springs are positioned in the cavity 33 which is provided in the upper part of the cylinder casing 22 above the portion 34 which is provided with a hole forming a bearing for the rod 27. The rod 27 is provided with a groove for receiving the expandable member 35 which retains a washer that functions as an abutment for the lower ends of the coil springs 31 and 32. The upper end of the lighter spring 31 abuts the lower surface of the plug 36 which is threaded into the upper part of the cylinder 22. The plug 36 is provided with a hole 36a which slidably receives the upper end of the rod 27.

When the motor (not shown) of the air compressor is started by connecting it to a suitable source of electric current supply, the parts of the valve device are positioned as shown in FIG. 1 and the check valve ball 14 is lodged against its seat 16 so that pressure of the compressed air in the tank connected to the threaded end 18 of the valve device is isolated from the compressor 10. At the same time the valve rod 27 is in the position shown in FIG. 1 so that the valve member 28 and O-n'ng 29 are away from the exhaust passage 26. The cavity 21 of the cylinder is thus vented to the atmosphere through the laterally extending exhaust ports 25.

Thus during starting of the air compressor 10 the air pumped thereby is exhausted from the main passage 12 through the constriction hole 19, passages 20, cylinder cavity 21 out to the atmosphere through passage 26 and exhaust ports 25. As the compressor motor gains speed, more air is supplied by the compressor 10 and air engaging the enlarged portion 30 of the rod 27 lifts this rod upward against the light spring tension of the coil spring 31. The enlarged portion 28 of the rod 27 is thus brought into the passage 26 and the O-ring 29 is brought against the end wall of the cylinder as shown in FIG. 2 so that the passage 26 is closed. At the same time, the heavier spring 32 is brought into engagement with the bottom of the plug 36. Closing the exhaust passage from the cylinder cavity leaves only the small bleeder passage 24 open to the atmosphere and substantially all the compressed air pressure is then applied against the check valve ball 14 so that this ball is dislodged from the seal surface 16 as shown in FIG. 2 and the compressed air output from the compressor is caused to move into the tank (not shown) through the line connected to the threaded end 18 of the valve device. When a predetermined pressure is achieved in the tank the compressor motor is turned off by a conventional air pressure switch. Check valve 14 is then closed. The pressure in cylinder cavity 21 is then gradually reduced because of the small leakage of air through bleeder passage 24 and when the pressure has fallen sufficiently channel 26 is opened. Heavier spring 32 breaks the seal of the O-ring 29 so that spring 31 moves rod 27 downward thereby opening the passage 26.

In FIG. 3 there is shown another embodiment of this device in which the cylinder 22a which corresponds to the cylinder 22 shown in FIGS. 1 and 2 is provided with a ball 37 of light material such as rubber or plastic. When the compressor is idle, the ball 37 will be at rest on the top of the screw 19a which is threaded into the upper part of the projection 11a. As the compressor gains speed, the compressed air furnished thereby lifts the ball 37 off of its rest position and moves it into the upper part 21a of the cylinder cavity which is slightly larger than the diameter of the ball. When the ball 37 is moved into the upper cavity 21a, it engages the rod 38. Rod 38 is provided with an enlarged head 39 which engages the lower end of the coil spring 40 that is positioned in a cavity 22b provided in the upper part of the cylinder block. The upper end of the spring 40 abuts a washer which is held in place by the expandable member 41 that is lodged in a groove formed in the upper part of the cavity 22b. The cylinder 22a is provided with exhaust passages 25a and 26a which are similar to passages 25 and 26, respectively, shown in FIG. 1. The passage 26a is slightly larger than the rod 38 so that air entering the cylinder cavity flows out through this passage and through the laterally extending holes 25a until the volume and the velocity of the compressed air flowing into the cylinder cavity is such as to raise the ball 37 up into cavity 21a and push the rod 38 upward against the tension of the spring 40 so that the ball 37 seals the passage 26a. With the passage 26a sealed, the check valve which corresponds to the spring loaded ball 14 shown in FIGS. 1 and 2 is open and compressed air is then supplied to the compressed air tank.

The graphs shown in FIGS. 4, 5 and 6 illustrate the operating characteristics of a compressor equipped with this invention. In FIG. 4 the lower part of the curve designated vent zone covers the start up of the compressor. The shift zone covers the torque-speed change during which the air is closing the valve controlling the exhaust passage. The graph shown in FIG. 5 shows three zones. Zone 0A shows the internal loss in the compressor. Zone A-B shows energy loss due to restricted air flow. Point B indicates closure of exhaust passage and Zone B-C is the zone in which compressor air pressure exceeds tank air pressure. Point C indicates tank pressure when air pressure switch opens. These curves show how the compressor motor is allowed to develop sufficient torque before the load is increased to full load. The curve shown in FIG. 6 shows the compressor performance.

While I have shown a preferred embodiment of the invention, it will be understood that the invention is capable of variation and modification from the form shown so that its scope should be limited only by the scope of the claims appended hereto.

What I claim is:

1. In a valve device for use on air compressors pumping air into a tank to reduce the load on the compressor until the compressor motor gains enough speed during starting so that the compressor can assume the full load, the combination comprising a valve casing having a main channel connected to the compressor and also connected to a tank for receiving the compressed air from the compressor a check valve in said main channel, said check valve being closed during starting of the air compressor, a cylinder having a cavity therein, means attaching said cylinder to said casing, a member extending into said cavity, said member being smaller than said cavity so that a passage exists around said member and between said member and the wall of said cavity, said casing having a restriction hole therethrough extending into said member, said member having air-spreading channels therethrough connecting said restriction hole to said passage, said cylinder having a normally open exhaust hole, a ball-shaped valve element in said cylinder cavity normally resting on said member, said ball-shaped valve element being smaller than said cavity so that a second passage communicating with said first mentioned passage exists around said valve element when said valve element is resting on said member, the flow of air from said air compressor during starting being through said restriction hole and through said air-spreading channels into said first mentioned passage and through said second passage into said exhaust hole, side surfaces of said valve element being exposed to said air flow through said second passage such that said valve element is raised from said member and closes said exhaust hole only after said air compressor approaches delivery of normal compressed air output, said check valve being opened by said normal compressed air output when said exhaust hole is closed by said valve element.

2. In a valve device for use on air compressors pumping air into a tank to reduce the load on the compressor until the compressor motor gains enough speed during starting so that the compressor can assume the full load, the combination as set forth in claim 1, further characterized in that said ball-shaped valve element seats around said exhaust hole, said cylinder having a second cavity with coil spring means positioned therein, means in said exhaust hole restraining said ball-shaped valve element from seating around said exhaust hole until the air flow through said cylinder cavity,

attains a predetermined pressure. 

1. In a valve device for use on air compressors pumping air into a tank to reduce the load on the compressor until the compressor motor gains enough speed during starting so that the compressor can assume the full load, the combination comprising a valve casing having a main channel connected to the compressor and also connected to a tank for receiving the compressed air from the compressor a check valve in said main channel, said check valve being closed during starting of the air compressor, a cylinder having a cavity therein, means attaching said cylinder to said casing, a member extending into said cavity, said member being smaller than said cavity so that a passage exists around said member and between said member and the wall of said cavity, said casing having a restriction hole therethrough extending into said member, said member having air-spreading channels therethrough connecting said restriction hole to said passage, said cylinder having a normally open exhaust hole, a ball-shaped valve element in said cylinder cavity normally resting on said member, said ball-shaped valve element being smaller than said cavity so that a second passage communicating with said first mentioned passage exists around said valve element when said valve element is resting on said member, the flow of air from said air compressor during starting being through said restriction hole and through said air-spreading channels into said first mentioned passage and through said second passage into said exhaust hole, side surfaces of said valve element being exposed to said air flow through said second passage such that said valve element is raised from said member and closes said exhaust hole only after said air compressor approaches delivery of normaL compressed air output, said check valve being opened by said normal compressed air output when said exhaust hole is closed by said valve element.
 2. In a valve device for use on air compressors pumping air into a tank to reduce the load on the compressor until the compressor motor gains enough speed during starting so that the compressor can assume the full load, the combination as set forth in claim 1, further characterized in that said ball-shaped valve element seats around said exhaust hole, said cylinder having a second cavity with coil spring means positioned therein, means in said exhaust hole restraining said ball-shaped valve element from seating around said exhaust hole until the air flow through said cylinder cavity attains a predetermined pressure. 